Cells and tissues may be immobilized and immunoisolated by three basic techniques: in extravascular chambers isolated but in the path of the blood stream, in spherical dispersions or microcapsules, and within macrocapsules. Using these techniques a great variety of cells and tissues of different animals have been immunoisolated and implanted in animals for development of therapeutic systems (reviewed by Christenson et al (1993)). Indeed, future applications of immunoisolated cell therapy are envisaged for diseases or conditions such as diabetes, hemophilia, hepatic failure, Alzheimer's, Parkinson's and Huntington's diseases, affective disorders, hepatic failure and fertility problems (Christenson et al, 1993). A complete review of the questions involved in encapsulation and immunoisolation is presented in a recent volume edited by Goosen (1993).
In the case of diabetes mellitus, alternatives to daily insulin injections have been searched for control of type I diabetes, or insulin-dependent diabetes mellitus (IDDM). These included pancreas transplants, pumps to deliver insulin under a controlled program and, more recently, Langerhans' islets transplantation. A review of sustained-release implants for insulin delivery has been published (Wang, 1991).
Several researchers have proposed different approaches to protect islet tissue from host attack after transplantation; these include encapsulation of islets in different materials such that insulin may be secreted but the beta-cells in the islet tissue will be immunologically isolated from the host. Polysaccharides have been proposed to form membranes, as is the case of agarose, by Howell et al(1982) or alginate, by Tze and Tai (1982). Materials used include synthetic poly-acids and polybases, gelatin and polyamino acids (Young et al, 1989) as well as different polysaccharides: chemically modified dextran, to form poly-ionically bonded capsules (Lim and Hall, 1988, PCT Int. Appl. WO 8,800,327), entrapment in alginate followed by stabilization with poly-lysine and alginate (Chang and Wong, 1992, U.S. Pat. No. 5,084,350), as well as a combination of chitosan and carboxy-methyl cellulose to form capsules of controlled permeability (Shioya and Hirano, 1990, U.S. Pat. No. 5,089,272).
Additionally, recent work bearing on regeneration of skin in culture has pointed out the important role of GAG's in the process, in studies where mixtures of collagen and GAG were used as support (Murphy et al, 1990; Yannas et al, 1990). Along the same line, keratinocytes and fibroblasts grown on a nylon mesh produced a dermal-like matrix containing proteoglycans (Slivka et al, 1993).
The importance of the extra-cellular matrix components for the normal development of the skin system lends support to a basis of the instant invention, e.g., that foreign molecules combined or structured with specified GAG's, e.g., preferably CIS in the case of this invention, will constitute ideal protecting materials in transplantation or implantation of cells or tissues of human or animal origin, with the purpose of treating or controlling disease
However, the art heretofore fails to teach or suggest the particular heteropolysaccharides polymer networks, and products therefrom and processes and uses of the invention.
Further, essential constituents of the extra-cellular matrix in connective tissues, of cell membranes and endothelial lining, and the overall presence of GAG's demonstrates their importance in matrix formation and extension, and in cell-matrix and cell-cell interactions. Although GAG's occur in an organism mostly linked to proteins, as proteoglycans, it has been demonstrated that only the protein portion is immunogenic; the glycosaminoglycan, e.g., CIS component, is not immunogenic by itself (Hirschmann and Dziewiatkowski, 1966; Loewi and Muir, 1965).
However, use of a GAG with an alginate salt, for instance GAG-alginate biomolecules, e.g., via a coupling reaction with a linker molecule, to form a heteropolysaccharide conjugate and products therefrom and processes and uses of the invention, are not heretofore taught or suggested. Moreover, the formation of a polymer network, e.g., of a semi-interpenetrating polymer network, based on the two components, alginate and GAG, e.g., CIS, rendered in gel form by addition of ions such as inorganic ions, e.g., calcium ions, has not been taught nor suggested in the prior art. Nor has a polymer network comprising a heteropolysaccharide from coupling GAG-alginate present in a GAG-alginate polymer network, been heretofore taught or suggested.
In the case of diabetes, the depth of interest in discovering the best way to use islets in transplantation is demonstrated by two recently published papers, one dealing with storage and preservation of islets (Jindal and Gray, 1994) and the other with the action of prednisone on the islet autograft function (Rodrigues Rilo et al, 1994).
U.S. Pat. No. 4,409,331 to Lim relates to the encapsulation of islets in polymeric material formed from alginate and poly-lysine; Lim and Sun (1980) discussed the microencapsulation of islets to form a bioartificial pancreas. Chitosan microspheres were developed that bind to GAG receptors on cell surfaces (Gallo et al U.S. Pat. No. 5,129,877). Collagen-GAG microcapsules were proposed as drug delivery systems, to deliver anti-microbial agents (Rase et al U.S. Pat. No. 5,169,631). Polyacrylates were also developed as encapsulation materials and have also been co-polymerized with alginate, as discussed by Stevenson and Sefton (1993). However, use of GAG with an alginate salt, GAG-alginate biomolecules, e.g., in physical mixture or bound via a coupling reaction with a linker molecule, to form a heteropolysaccharide or a physical network, e.g., s-IPN, gel and products therefrom and processes and uses of the invention, are not taught or suggested.
It is emphasized, however, that none of the art heretofore has GAG acted as the major biocompatibility agent between a foreign chemical structure or device and host organism, especially in a composition with an alginate.
The synthesis and properties of glycoconjugates has been reviewed in a book edited by Lee and Lee (1994). The new class of structures now being described herein belongs to a group of glycopolymers formed by joining together two different natural heteropolysaccharides by reaction with an unnatural tether.e.g., divinyl sulfone. This new class would enter the list of neoglycoconjugates compiled by Magnusson et al(1994) under the heading "glycopolymers with gel forming properties".
On the other hand, the physical gel formed by adding calcium ions to solutions containing variable concentrations of GAG, e.g., CIS, and alginate belongs to the group of polymers known as semi-interpenetrating polymer networks, recently discussed by LaPorte (1997). In this category, one type of polymer is enmeshed and entrapped by a second polymer, which is cross-linked to stabilize the structure.
However, that compositions of the invention may be characterized as "glycopolymers with gel forming properties" or as a "polymer network", e.g., "a semi-interpenetrating polymer network" does not mean that the invention has heretofore been taught or suggested.